System and method for paging off-line state terminals

ABSTRACT

A communications terminal is arranged to transmit/receive data to/from a mobile communications network. A mobility manager tracks a location of a communications terminal within the mobile communications network for routing data to or receiving the data from a communications terminal via a radio network part in accordance with context information of the communications terminal, and the mobile communications network includes a virtual mobility manager. The communications terminal is configured to transmit an indication that the communications terminal is entering an off-line state, and the virtual mobility manager, in response to that indication, can store at least part of the context information of the communications terminal, upon a triggering event occurring, to receive a paging message from the virtual mobility manager at the off-line communications terminal, and to establish with mobile communications network a communications bearer, for communicating the data after the communications terminal has moved to an attached state.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to British Patent Application1120151.4, filed in the UK IPO on Nov. 22, 2011 and British PatentApplication 1120152.2, filed in the UK IPO on Nov. 22, 2011, the entirecontents of each of which being incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to communications terminals forcommunicating data to and/or from communications terminals and methodsfor communicating data.

Embodiments of the present invention provide a technique for managingcommunications terminals in an offline state to facilitate proceduresinitiate by either a mobile communications network or the mobilecommunications terminals to enable data transfers on either the uplinkor the down link.

BACKGROUND

Wireless mobile telecommunication systems such as the 3GPP defined UMTSand LTE systems have been designed to provide high data rate mobilecommunication services to users of communication terminals.Conventionally an LTE network would be expected to provide communicationservices to communication terminals such as smartphones and personalcomputers (e.g. laptops, tablets and so on). These types ofcommunication services are typically provided with high performancededicated data connections optimised for high bandwidth applicationssuch as streaming video data. However, recent developments in the fieldof machine type communication (MTC) (sometimes referred to as machine tomachine (M2M) communication) have resulted in more diverse applicationsbeing developed to take advantage of the increasing ubiquity of mobiletelecommunication networks. As such it is increasingly likely that anLTE network will also be expected to support communication services fordevices such as smart meters and smart sensors. Devices such as these,generally classified as “MTC devices”, are typically less complex thanconventional LTE communication terminals such as smartphones andpersonal computers and are characterised by the transmission andreception of relatively low quantities of data at relatively infrequentintervals.

However, certain aspects of LTE type systems are not optimised for theoperation of MTC devices. For example, generally LTE communicationterminals exist in one of two logical states: attached or detached. Inthe detached state, the communication terminal is typically eitherpowered off or de-registered if out of range of the network for a longtime. In the attached state the location of the communication terminalis monitored by the network and the device also remains powered up readyto receive paging messages from the network.

This can be inefficient for MTC devices, particularly if they aredeployed in large numbers. Firstly a large quantity of network resourcewould be required to support a high number of devices and secondly, inorder for an MTC device to stay in the registered state, it is requiredto keep its transceiver circuitry powered up to monitor the pagingchannels. In low complexity devices which may not have access to anexternal power supply, this power consumption may be undesirable.

Accordingly, efforts have been made to define a new “offline” statespecifically for MTC type devices. In the offline state it is intendedthat MTC devices can still be paged but the amount of network resourcethat is required to support the offline state is reduced along with theamount of power consumed by the MTC device when in the offline state.However, so far, conventional LTE network architecture does not supportthe offline state.

SUMMARY OF THE INVENTION

According to the present invention there is provided a communicationsterminal for transmitting data to and receiving data from a mobilecommunications network. The mobile communications network includes aradio network part having a plurality of base stations arranged totransmit data to and receive data from the communications terminal via aradio access interface, and a core network part which includes at leastone packet data network gateway which is arranged to route data to andreceive data from the base stations of the radio network part via thecore network. A mobility manager is arranged to track a location of thecommunications terminal within the mobile communications network forrouting the data to or receiving the data from the communicationsterminal via the radio network part in accordance with contextinformation of the communications terminal, and the mobilecommunications network includes a virtual mobility manager. Thecommunications terminal is configured to transmit an indication that thecommunications terminal is entering an off-line state, the virtualmobility manager being configured, in response to the indication thatthe communications terminal has entered the off-line state to store atleast part of the context information of the communications terminal,upon a triggering event occurring, to receive a paging message from thevirtual mobility manager at the off-line communications terminal, and toestablish with mobile communications network a communications bearer,for communicating the data after the communications terminal has movedto an attached state. An improvement can be provided when thecommunications terminal enters the offline state, because the locationof each terminal is not tracked when changing designated tracking areasor a set of tracking areas and so paging can be co-ordinated by a higherlevel virtual mobility manager rather than a lower level mobilitymanager.

In accordance with a first aspect of the present invention, there isprovided a mobile communications system comprising one or more mobilecommunications terminals operating with a mobile communications network.The mobile communications network comprises a radio network partincluding a plurality of base stations arranged to transmit data to andreceive data from the one or more communications terminals via a radioaccess interface, and a core network part. The core network partincludes at least one packet data network gateway which is arranged toroute the data to and receive the data from the base stations of theradio network part via the core network and a mobility manager arrangedto track a location of the communications terminals within the mobilecommunications network for routing the data to or receiving the datafrom the communications terminals via the radio network part inaccordance with context information which is stored for each of the oneor more communications terminals. The mobile communications networkincludes a virtual mobility manager which is configured to store atleast part of the context information of a communications terminal whenthe communications terminal enters an off-line state so that if atriggering event occurs when the communications terminal is in theoff-line state, the virtual mobility manager can page the off-linecommunications terminal in the off-line state so that a communicationsbearer can be established with the communications terminal, using thestored context information, for communicating the data after thecommunications terminal has moved to an attached state. The off-linestate may for example correspond to a state in which the communicationsterminal reduces an amount of data communicated to or received from themobile communications network.

Embodiments of the present invention can provide an improved techniquefor implementing an offline state for communications terminals operatingwith a mobile communication network. In particular, an improvement isprovided when the communications terminal enters the offline state,because the location of each terminal is not tracked in the sense thatthe communications terminal is not required to inform the network whenchanging designated tracking areas or a set of tracking areas and sopaging can be co-ordinated by a higher level virtual mobility managerrather than a lower level mobility manager. As a result, a load on themobility manager can be reduced. This reduces a likelihood of themobility manager being overburdened with tracking the location of alarge number of communications terminals in the offline state andenables it instead to remain dedicated to communications terminals inthe conventional attached state.

The virtual mobility manager may be arranged to store a unique identityof the off-line communications terminal and following a trigger event,the virtual mobility manager is arranged to send a paging command to theradio access part including the identity of the off-line communicationsterminal, and the base stations are arranged to transmit a pagingmessage including the identity of the off-line communications terminal.

In conventional mobile telecommunication systems it is consideredundesirable to implement a “global” paging scheme whereby an entirenetwork is paged when downlink data is received by the network forcommunication to terminals when the location of the terminal is unknown.Usually, should such a scheme be implemented in a large network, thedownlink channel of each cell could quickly become overloaded withpaging messages. Thus, in many conventional mobile telecommunicationsystems such as those based on the LTE network architecture, thelocation of each communications terminal in the connected state (orequivalent) is monitored by the network at least to the resolution ofthe tracking area or a set of tracking areas contained in a trackingarea list. This enables paging messages to be routed to a part of thenetwork corresponding to a tracking area where a communications terminalis located without having to transmit paging messages in every cell. Incontrast with conventional mobile telecommunication systems, inaccordance with embodiments of the present invention it has beenrecognised that an identity associated with communications terminals inthe offline state can advantageously be stored at a virtual mobilitymanager thereby facilitating a global paging scheme using for examplethe packet data network (PDN) gateway. The offline state has beenproposed in view of certain types of terminals, for example MTC typedevices, although not exclusively, which typically transmit and receiveonly small quantities of data. Therefore the frequency with which pagingmessages are sent to certain types of terminals is likely to becomparatively low compared to other types of terminals. Furthermore,network operators may chose to restrict the transmission of data tothese types of communications terminals to times at which the network isless busy with conventional data traffic. Consequently, implementing aglobal paging scheme for some type of terminals would not necessarilyincrease the load on the downlink channels beyond tolerable levels.Moreover, using a global paging scheme to support the offline stateprovides certain advantages, not least removing the requirement that thelocations of communications terminals in the offline state are tracked.

In some examples, the mobility manager may be configured to detect thatthe communications terminal has entered the off-line state, and upondetecting that the communications terminal has entered the off-linestate, to transmit the at least part of the context information of theoff-line communications terminal with the unique identity associatedwith off-line communication terminal to the virtual mobility manager.The virtual mobility manager may be configured to store the at leastpart of the context information communicated from the mobility managerin association with the unique identifier for the off-linecommunications terminal.

In some examples, the virtual mobility manager may be configured, afterreceiving the at least part of the context information from the mobilitymanager to generate a second unique identifier, to communicate thesecond unique identifier to the off-line communications terminal, and tostore the at least part of the context information with the secondunique identifier. For example, the first unique identifier and thesecond unique identifier are global unique identifiers (GUTI), and thesecond unique identifier may be based on the first unique identifier.

In some examples the triggering event which causes to virtual mobilitymanager to arrange for the mobile communications terminal to be pagedmay include for example at least one of the packet data network gatewayreceiving data for communicating to the off-line communicationsterminal, the mobile communications network receiving control plane datafor communicating to the off-line communications terminal, the off-linecommunications terminal moving from the off-line state to the attachedstate in response to a user command or the off-line communicationsterminal moving from the off-line state to the attached state in orderto communicate data to the mobile communications network.

In some example embodiments global paging of the whole mobilecommunications network or a plurality of networks may not be implementedfor the whole network or networks contemporaneously, if a communicationsterminal being paged is known to be receiving or transmitting delaytolerant data. For example, for MTC devices global paging at the sametime may not be required as such devices usually handle delay toleranttraffic.

According to some examples the mobile communications network is arrangedto implement a hierarchical paging scheme in which the PLMN area isdivided into regions. A first of the regions to which the communicationsterminal was last attached is paged first because it is most likely thatthe communications terminal has not roamed from this tracking area.However if the communications terminal is not successfully paged withthis first tracking area, because no acknowledgement is received fromthe communications terminal, then other regions are selected to bepaged. This selection may be done in different ways, for examplegeographical proximities e.g. in circles covering larger regions butexcluding the region which has been paged, or in squares (but this iswith the granularity of the tracking area), or based on current load ofthe paging channel in some designated regions.) This can be asubstantial benefit in certain types of networks, particularly thosewhich contain a high number of terminals that are likely to be in theoffline state.

As explained above, in accordance with examples of the presentinvention, the virtual mobility manager that manages paging forterminals in the offline state is in one example not a network elementwith mobility tracking functionality, for example an LTE mobilitymanagement entity i.e. the MME or in the 2G/3G system for data servicesthe SGSN, but is a higher level network gateway which does not track thespecific location of each terminal within the network and instead simplymonitors which terminals are in the offline state. In one example thevirtual mobility manager is associated with a PDN-GW, in the sense thatit is anchored to the functionality of the PDN-GW. Anchoring this pagingfunctionality at the network gateway enables the mobility managemententity to devote more resource to managing the paging of terminals inthe conventional attached state because, for example, communicationsterminals in the offline state no longer need to be tracked. Otheradvantages include obviating or reducing a requirement to establishbearers via the NAS signalling as the network is capable of restoringcommunications bearers, when the transition from the Offline toRegistered state occurs, and the communications terminal retains bearerinformation in the offline state whereas in the de-registered state thisbearer information is lost there could be one or more bearersestablished. This is also applicable to the UMTS/2G as the PDN contextmay be still established when the communications terminal is moved tothe offline state. Moreover, the number of terminals that can besupported in the offline state is limited only by the capacity of thenetwork gateway interface to maintain a record of which terminals arecurrently in the offline state.

In some embodiments the virtual mobility manager may be co-located witha packet data network gateway of the telecommunications network PDN-GW.The virtual mobility manager is a separate logical entity from thenetwork gateway. As will be appreciated the mobility manager and aserving gateway may or may not be co-located depending on the design.However they are two separate logical entities.

Various further aspects and features of the invention are defined in theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram showing an example of a conventionalmobile telecommunication system based on the 3GPP defined Long TermEvolution (LTE) system architecture;

FIG. 2 provides a schematic diagram showing an example of a mobiletelecommunications system arranged in accordance with an example of thepresent technique;

FIGS. 3a and 3b provide schematic diagrams illustrating state machinesimplemented at the network and a communications terminal respectivelyarranged in accordance with an example of the present technique; and

FIG. 4 provides a schematic diagram showing an example of thecomposition of a conventional Globally Unique Temporary Identifier(GUTI);

FIGS. 5a and 5b provides a call flow diagram illustrating an exampleembodiment of the present technique illustrating operations of acommunications terminal and a mobile communications network when thecommunications terminal enters an off-line state;

FIGS. 6a and 6b provides a call flow diagram illustrating an exampleembodiment of the present technique illustrating operations of acommunications terminal and a mobile communications network when thecommunications terminal changes from an off-line state to an attachedstate;

FIGS. 7a and 7b provides a call flow diagram illustrating an exampleembodiment of the present technique illustrating operations of acommunications terminal and a mobile communications network when thecommunications terminal provides the communications network with anupdate of its presence when in an off-line state;

FIG. 8 provides a schematic illustration of example mapping of corenetwork entities which are employed when a communications terminalenters an off-line state; and

FIG. 9 provides a schematic illustration of the core network entities ofFIG. 8 which show the example mapping of entities when thecommunications terminal enters an attached state.

DESCRIPTION OF EXAMPLE EMBODIMENTS Conventional LTE Network

FIG. 1 provides a schematic diagram of a conventional mobiletelecommunications network arranged in accordance with the Long TermEvolution (LTE) 3GPP architecture standards. The LTE network includes acore network part 101 connected to a plurality of base stations 102referred to in the art as an enhanced Node Bs (eNode B). The eNode Bs102 are arranged to transmit data to and receive data from one or moreterminals 103 via a radio interface. The terminals 103 are generallyreferred to as “communications terminals” which can include devices suchas mobile phones, smart phones, data cards and so on.

The LTE core network 101 includes a serving gateway (S-GW) 104 which isarranged to route data to and from the eNode B 102. The serving gateway104 is connected to a packet data network gateway (PDN-GW) 105 whichroutes data into and out of the LTE core network from an externalnetwork 107. The LTE core network 101 also includes a mobilitymanagement entity (MME) 106 connected to the serving gateway 104 whichis responsible for authenticating communications terminals 103attempting to access the LTE network by retrieving subscriber profileand authentication information stored in a home subscriber server (HSS)(not shown). Typically the MME 106 is also connected to the eNode Bs102. Although not shown in FIG. 1, as is known in the art, usually anLTE based mobile telecommunications network will include more than oneS-GW and more than one MME. Moreover, the network will typicallycomprise many hundreds if not thousands of eNode Bs. The eNode Bs can begrouped together to form tracking area(s) which are served by a specificMME and S-GW(s).

As is known in the art, a conventional LTE mobile telecommunicationnetwork comprises further network elements such as a Policy and ChargingRelated Function (PCRF) and Policy and Charging Enforcement Function(PCEF) which amongst other entities they constitute the Policy Controland Charging (PCC) subsystem; however for the sake of brevity these havebeen omitted.

Conventional Communications Terminal States

A communications terminal is usually in one of three states: detached,idle or connected. An LTE communications terminal typically is initiallyin the detached state, then transitions to the connected state and thentransitions between the connected state and the idle state. This processis explained in more detail below. In the detached state, thecommunications terminal 103 is usually switched off or in the so called“flight-safe mode” state or in the process of attempting to attach tothe network or out of range of the network coverage area for a long timewhich will result in the network performing an implicit detach. In anycase, the location of the communications terminal is unknown to thenetwork and it cannot be paged. In the idle state, the communicationsterminal 103 has been authenticated and has attached to the network butis not transmitting or receiving any data packets. When in the idlestate, the tracking area(s) which indicate a current location of thecommunications terminal 103 is stored in the MME 106. Thus when in theidle state the communications terminal 103 is required to notify itscurrent location by initiating C-Plane signalling. The trigger is whenthe communications terminal has changed the tracking area or currentlyassigned set of tracking areas. Whilst no further information about thecommunications terminal 103 is stored at the eNB, there is acommunications terminal context stored at the S-GW.

When in the connected state, the coverage area/cell in which thecommunications terminal 103 is located is known by the MME so that datapackets can be routed via the S-GW 104 and the eNB 102 to and from thecommunications terminal 103. The communications terminal 103 also has aradio resource connection with the eNode B 101 so that dedicated uplinkand downlink radio resources can be specifically assigned to thecommunications terminal. In both the idle and the connected states, thelocation of the communications terminal is known (although notnecessarily within a specific cell) and the communications terminal canbe paged by the network when it is in the IDLE state (Note: in UMTS itis possible to send the paging message in the “connected” state in somescenarios).

In 23.368 further explanations were given to the meaning of“offline/online” terminals which is quoted below:

-   -   Online: “Online” means the MTC Device is attached to the network        for Mobile Terminated (MT) signalling or user plane data.    -   Offline: When the MTC Device is “offline” (i.e. detached) the        MTC Device can listen to trigger indications on for example a        broadcast or paging channel.

There are a few service requirements in 22.368 which assume the systemis able to manage terminals which are in the “offline” state. They areas follows:

-   -   Common service requirement: MTC devices may be kept offline or        online when not communicating, depending on operators policies        and MTC application requirements    -   Device Triggering: Receiving trigger indication when the MTC        device is offline    -   Location Trigger: The network shall be able to initiate a        trigger to the MTC device based on the area information provided        by the network operator and the network may apply location        specific triggers when the MTC device is offline (it is assumed        that the area covered is based on the characteristics of the        radio access network e.g. a cell or a group of cells)    -   Infrequent transmission:        -   The network shall establish resources only when transmission            occurs        -   When there is data to transmit/receive, the MTC device shall            connect to the network, transmit and/or receive the data            then return to an offline state            Network Implementation for Offline State

As will be explained in the following passages, example embodiments ofthe present invention can provide a technique for addressing a technicalproblem of notifying communications terminals in the offline state toestablish a bearer for communicating data to the communicationsterminals.

Conventionally, if downlink data addressed to a communications terminalin the idle state is received at the PDN-GW 105, the PDN-GW forwards thedata to the S-GW which notifies the MME about the pending downlink datafor the delivery to the communications terminal then a paging command isgenerated by the MME 106 and sent to all relevant eNode Bs 102 in therelevant tracking area. The eNode 102 then transmit a paging message.Upon detection of the paging message, the paged communications terminal103 transitions to the connected state and the MME establishes thenecessary U-Plane connections with the communications terminal 103, eNB102 and the S-GW 104 to receive the downlink data. However the triggerfor establishing the U-plane data path comes from the communicationsterminal when it responds to the paging message. As will be explainedfurther below, in accordance with examples of the present technique, theGUTI allocated to a communications terminal is adapted for the purposeof communications terminal identification during paging and for thepurpose of routing of the control plane signalling to appropriate nodesin the network.

FIG. 2 provides a schematic diagram showing a telecommunication networkarranged in accordance with an example of the present technique.

The telecommunication network shown in FIG. 2 includes elementscorresponding to those present in the conventional telecommunicationsystem shown in FIG. 1. These elements are numbered in correspondencewith those shown in FIG. 1. However, the network shown in FIG. 2includes an adapted core network 303, which operates with a radionetwork part 304 to communicate data to and from the communicationsterminals 103. In FIG. 2, control or C-plane interfaces are shown withdashed lines, whereas user or U-plane interfaces are shown with solidlines.

As shown in FIG. 2, the core network part of the telecommunicationssystem includes a Virtual Mobility Management Entity (VMME) 301 coupledto a Packet Data Network Gateway PDN-GW 302. For clarity the functionsof the VMME 301 and the PDN-GW 302 will be described separately.However, it will be understood that in some examples the VMME 301 andthe PDN-GW 302 can be implemented as a single logical entity.

The radio network part of the communications shown in FIG. 2 provides aheterogeneous wireless access network in that the radio network part 304also includes infrastructure components from a 2G/GPRS network such as aServing Gateway Support Node (SGSN) 320 an a radio network controller(RNC) and base station (NodeB) 322 as well as infrastructure componentswhich form a wireless access interface according to the LTE standardexplained above with reference to FIG. 1. In addition a Virtual ServingGateway Support Node (VSGSN) forms part of the core network 303 forcommunicating data to and from the SGSN 320. As shown in FIG. 2, thePDN-GW 302 is connected to the SGSN 320 a Gn interface 326, the VSGSN324 is connected to SGSN 320 via a Gn′ interface 328 and the VMME 301 isconnected to the SGSN 320 via a modified S3′ or S4′ interface 308. Theinterface 328 and the SGSN 320 may be modified to allow legacyinfrastructure equipment according to for example a 2G/GPRS standard tooperate with the VSGSN 324 which functionally is similar to the VMME301. This is explained below.

As shown in FIG. 2, the VMME 301 includes an S11′ interface 307 whichconnects it with the MME 106 or a connection to the MME 106 may beachieved more conventionally via the S-GW 104 via an S-11 interface 309and an S5 interface 311. The PDN-GW 302 is also provided with a Gx′interface for communicating with the VSGSN 324 and/or an Sx′ interfacefor connecting to the VMME 301. In some examples the Sx′ may not berequired, for example if there is a one to one mapping between thePDN-GW 301 and the VMME 301 and the PDN-GW 301 and the VMME 301 areco-located.

The network of FIG. 2 also includes a PLMN Gateway (PLMN-GW) 305, whichis connected to an external network and may receive control plane(C-plane) triggers identifying that there is a requirement tocommunicate signalling data to a communications terminal 103. Thefunctions of the VMME 301, the PDN-GW 302 and the PLMN-GW 305 areexplained below with reference to the implementation of the offlinestate.

Offline State

Conventionally, a communications terminal is in either the connected oridle state (collectively referred to as the attached state) or in thedetached state. In the attached and idle states the communicationsterminal can be paged and information regarding the location of thecommunications terminal is stored in the MME of the network. At the veryleast the tracking area or a set of tracking areas within which thecommunications terminal is known. On the other hand the detached state,the communications terminal is, effectively, completely disconnectedfrom the network in that its location is not tracked and it cannot bepaged, nor can the ingress IP flow be associated with the communicationsterminal, so routing of data is not possible.

In accordance with the present technique, conventional networkfunctionality is adapted to support a further offline state. In theoffline state, in contrast with the conventional idle and connectedstates, the location of the communications terminal is not trackedwithin the network but the communications terminal and the network isarranged so that the communications terminal can still be paged. Thenetwork is also able to establish means to route data. As will beexplained below, in order to facilitate this arrangement, when acommunications terminal moves to the offline state and its location isno longer tracked by the network, the VMME 301 stores the communicationsterminal's EPS MM context with the old GUTI, a new GUTI is allocated andis used in signalling initiated by the communications terminal and thenetwork. For example a modified location update procedure is used toreport periodically a communications terminal's presence to the PLMN aswell as paging.

When a communications terminal is required to enter the offline state,the network (MME) requests the VMME to establish the communicationterminal's EPS MM context and then it sends an offline state updatemessage to the communications terminal 103 informing the communicationsterminal 103 that it shall be entering the offline state.

As described above, the MME 106 allocates a GUTI for everycommunications terminal active in the network which is controlled bythis MME. When the MME 106 takes the decision to move the UE 103 to theoffline state or it is requested to do so by the network, it sends acommunications terminal offline notification message to the VMME 301.This message includes the communications terminal's EPS MM contextinformation with the GUTI of the communications terminal. In someexamples, the MME 106 then deletes or caches the EPS MM contextinformation associated with the communications terminal along with allother information associated with the communications terminal when itwas attached.

When the VMME 301 receives the state update message, the GUTI of thecommunications terminal entering the offline state is discarded by theVMME, and the VMME creates a new GUTI for the communications terminal.However the new GUTI includes the mobile country code (MCC) and mobilenetwork code (MNC) of the communications terminal. The new GUTI is thencommunicated to the communications terminal by the VMME 301 via the MME106. The IP address associated with the communications terminal which ismoved to offline state is kept and stored at the PDN-GW (also referredto as PDN-GW) as part of the context information for the communicationsterminal. For communications terminals entering the offline state thecontext information maintained is a sub-set of the context informationin the on-line state because some of the fields are not relevant.

Typically this is performed by the VMME 301. The PDN-GW 302 maintainsrecords with the context information of all registered communicationsterminal's also these in the offline state. The context informationbesides other information has the IP address associated with thecommunications terminal and a new indication whether the communicationsterminal is in the offline or registered state.

As will be appreciated the IP address may also be allocated by theexternal network, in which case conventionally the PDN-GW stores the IPaddress. However a tunnel is established between the ISP (InternetService Provider) and the PDN-GW. This tunnel is not removed when thecommunications terminal is moved to the offline state nor thecommunications terminal's context information at the PDN-GW is removed.However all other operations remain the same.

Paging Communications Terminals in the Offline State

In the conventional system an entity is selected to coordinate thepaging procedure. In the LTE/EPC it is always the MME, in UMTS it isalways the SGSN. The table below presents in detail of how the systemselects the paging co-ordination entity based on the informationavailable for the communications terminal.

Paging cordination entity COMMUNICATIONS COMMUNICATIONS PLMN TERMINALSTATE: TERMINAL STATE: KNOWN ROAMING ATTACHED OFFLINE Yes No MME VMME(see No SGSN VMME (if the S3′ or note 1) S4′ are supported) or VSGSN (iflegacy node) Note 1: It is assumed that the PLMN in which thecommunications terminal resides is known and it is the home PLMN.

As shown in FIG. 2 notification for paging can be triggered by theU-Plane data arrival 340 or by the C-plane signalling 330 coming from anexternal entity. The former solution is desirable as the applicationserver does not need to have additional complexity to handle andco-ordinate the paging/notification procedure.

As presented in the FIG. 2 according to the present technique some newinterfaces are introduced into the architecture of the mobiletelecommunications network, which are:

-   -   Sx′ interface 309 (which can be internal, which can be typically        based on the diameter protocol),    -   S11′ interface 307 based on the S11 interface (based on the        extended GTPC protocol)°    -   S4′ interface 308 based on the C-Pane part of the S4 interface        (based on the extended GTPC protocols) or the S3′ interface    -   Gn′ interface based on the C-Pane part of the Gn (based on the        GTP-C protocol) and is used to interwork with the legacy SGSN).    -   Gx′ interface (which can be internal which can be typically        based on the diameter or GTP-C protocol)

Furthermore some additional functions are introduced which are:

PDN-GW: The PDN-GW 302 functional entity has a new function to requestthe paging for the offline terminals when the location of thecommunications terminal is known with the granularity of the home PLMN.The MM context information is pushed to the VMME via the PDN-GW when theterminal is moved into the Offline state. The PDN-GW can also be thoughtas a proxy MME or virtual MME (VMME) for the communications terminal inthe MM_Offline state in the case when the VMME and PDN-GW areco-located. This node is also an anchor point for any data coming fromthe PDN networks. Please note there might be several PDN-GWs used by thecommunications terminal and all of them will support these enhancedfunctions.

VMME: The VMME 301 is a logical entity which stores the UE's MM contextinformation (or a subset of it) when the mobile communications terminalis in the offline state. The VMME also initiates and supervises thepaging procedure for the terminals in the offline state and may assistin the establishment the bearers when the terminal is to be moved backto the attached state. The VMME assists a new serving MME in thecreation of the communication terminal's MM context information based onits stored UE's context data.

PLMN-GW: The PLMN-GW 305 is a C-Plane entity which is accessible fromthe outside of the HPLMN for communication with the VMME entit(y/ies).When the application residing on the application server, the amount ofinformation exchanged from the PLMN may be restricted. As such it may bemore difficult to push the MM_context information to this entity due tooperators concerns. However the PLMN-GW 305 is used by the applicationserver to trigger the paging procedure in the PLMN (e.g. the PLMN-GWcontacts the VMME).

As will be appreciated from the explanation above for U-plane andC-plane triggering 330, 340 can be made by the U-Plane data arrival orby the C-plane signalling coming from the external to the PLMN entity.The former solution is desirable as the application server does not needto have additional complexity to handle and co-ordinate thepaging/notification procedure. The latter can be used also to addressmore generalized scenario when the PLMN is not known or thecommunications terminal is not allocated the IP address by the HPLMN.

The communications terminal 103 in the Offline state still has the IPaddress(es) allocated despite introduction of a new MM-Offline state.The PDN-GW 302 is a suitable entity to be the first point of contact fordata arriving to the PLMN. One advantage is that this architecture islinked with the subscription controlled by the PLMN. The VMME logicalentity will likely be under the control of the PLMN operator in the sameway as the PDN-GW is.

The C-Plane approach requires the trigger to come from the applicationresiding on the application server. That requires the application tohave a reachability status of the communications terminal.

The U-Plane based triggers approach conceals this information from theapplication server as there is no need to disclose it to the applicationserver because the VMME is managed by the Home PLMN. Where as thePLMN-GW helps the operator to conceal some network information fromthird parties when the C-Plane triggers are used.

In the following examples, the VMME 301 and PDN-GW 302 respond to a“trigger event” to cause a global paging message to be transmittedthroughout the network.

The paging procedure depends on whether some assumptions can be made onthe location of the communications terminal:

-   -   The communications terminal's current location within the PLMN        may or may not be known. For the offline terminals it is assumed        that the location of the communications terminal is not known or        can not be ascertained with confidence. However the tracking        area(s) where the UE was last seen or the tracking area(s) where        the communication terminal is located during reporting its        presence may be used to restrict the initial scope of the paging        message distribution to allow “intelligent” hierarchical paging.

The PLMN in which the communications terminal resides is assumed to beknown for the example of non-roaming scenarios, which thereforecorresponds to the Home PLMN. In this example, the communicationsterminal is in the offline state in which paging is triggered across thewhole home PLMN. For example this could be achieved using the cellbroadcast (the so called the CBC), the BCCH channel, the MBMS system ifavailable (e.g. the MCCH) or the legacy or a new paging channel with thelong/extremely Long DRX cycles.

The paging procedure facilitates the system in the following:

-   -   Locate/notify the communications terminal within the PLMN    -   Once the communications terminal contacts the network and the        PDN-GW the S5/S1/radio bearers are established    -   The VMME pushes the context back to the MME which triggers the        MME. Then the 85 bearer(s) are established. The MME coordinates        the establishment of the bearers as in the legacy architecture        i.e. S1/Radio Bearers (MME+eNB). Once the VMME has triggered the        S5 bearer(s) to the PDN-GW(s) to be established, the other        VMME(s) shall remove their MM context(s).

If the legacy global paging is used the system may employ pagingstrategies. For example, the system may page certain geographicalregions/areas selectively as it is likely that communications terminalswill generate delay tolerant traffic. However it may also be preferableto contact the communications terminal in the shortest time possiblewhich would require more rapid paging response by reducing the number ofpaging stages. In the extreme case a global paging is used.

The examples of U-plane triggering shown and C-plane triggering shown inFIG. 2 will be explained in more detail in the following sections:

User Plane Trigger Example

As will be understood, the communications terminal is paged if there isdownlink control data or downlink user data to be received. In thedownlink user data case, the PDN-GW 302 is arranged to route downlinkdata packets from sources which may be routed from the external network.If an ingress data packet is detected with a destination IP addresscorresponding to one of the offline mode communications terminals, thePDN-GW 302 is arranged to send an alert message to the VMME 301. In someexamples the alert message includes an indication of the identity of theoffline state communications terminal associated with the detected IPaddress in the data packet as the PDN-GW holds the UE's contextinformation for the terminals in the offline state.

Upon receipt of the alert message, the VMME 301 identifies the modifiedGUTI associated with the offline state of the communications terminal towhich the incoming data packet is addressed and triggers a pagingcommand via the MME 106 to all the eNodebs 102 in the network. Thepaging command typically includes the GUTI or at least some part of theGUTI that can uniquely identify the communications terminal such as theM-TMSI+VMME identifier or the S-TMSI+MME Group ID (optionally ifdistinct VMME codes are used in the system). In a conventional systemthe S-TMSI is used to page in the E-UTRAN, the GUTI is used in the Core.In this case the RAN paging needs to be extended to include also the MMEGroup id if there are several VMMEs in the system.

It will be understood that although the diagram of FIG. 2 shows only asingle MME 106, in larger networks there may be multiple MMEs. In thiscase, all the MMEs will trigger the transmission of the paging message.In some examples, the trigger may be delivered via the direct interfacebetween the VMME and the MME (S11′ interface) or might be delivered viathe modified protocol messages over the S5/S11 interfaces and the Sx′interface 309.

Upon receipt of the paging command, each eNB 102 transmits a pagingmessage within its cell in accordance with a conventional arrangement.Once a communications terminal in the offline state receives a pagingmessage including an identifier that it recognises as its own, thecommunications terminal is operable to transition to the attached stateincluding transmitting a service request and thereby establishing therequired logical connections to receive the downlink data. During thisprocedure, signalling data confirming successful receipt of the pagingmessage is sent from the communications terminal to the VMME 301 via theMME 106. The GUTI allocated by the VMME is used by the MME to route theresponse to the VMME. The VMME 301 is then arranged to send thecommunications terminal's EPS MM context information to the MME 106which in the case there are multiple S-GWs selects the appropriate S-GW104 and establishes the appropriate S5 bearers with the PDN-GW 302according to a conventional arrangement. At this stage the MME 106updates the communications terminal's EPS MM context information. Thecommunications terminal's PDN-GW context information is also updated toreflect new information such as e.g. the S-GW used to terminate the S5interface. Upon successful establishment of these bearers the VMME 301deletes the old EPS MM context information associated with thecommunications terminal that was stored when the communications terminalentered the offline state. The MME 106 then proceeds to establish theappropriate S1 bearers as is known in the art and establish the relevantradio connections which trigger the communications terminal totransition to the connected state. The MME 106 allocates to thecommunications terminal a new GUTI which is signalled to thecommunications terminal and the old GUTI is deleted. Similarly, thecommunications terminal discards the old GUTI if a new one has beenallocated.

Control Plane Trigger Example

The user plane example is based on the PDN-GW 302 triggering the pagingprocess by recognising incoming packets (the ingress to the EPS network)addressed to a communications terminal in the offline state. However, insome examples, particularly the transmission of downlink control data,rather then using the PDN-GW 302 as the paging coordination entity anapplication can be located on the application server 304 which canrequest that the communications terminal is paged.

In this example, rather than the paging process being triggered by thePDN-GW 302 detecting an appropriately addressed downlink data packet,the PLMN-GW 305, connected to the application server 304 triggers thepaging process by sending a paging request message to the VMME 301. Oncethe paging request message is received by the VMME 301, the pagingprocess is commenced as described above for the user plane data example.

In some examples, when generating the paging request, the PLMN-GW 305will use the IMSI of the communications terminal. In other examples, thePLMN-GW will use another identity (e.g. fully qualified Domain Name(FQDN), URI (Uniform Resource Identifier) or URN (Uniform ResourceName)) which the PLMN can map onto communications terminal's IMSI. Whenthe VMME 301 has determined that the paging process has been successful,the VMME 301 sends a confirmation message to the PLMN-GW 305 whichinforms the application server 304 as appropriate.

State Machines for the Offline State

In some embodiments a state machine representing the operation ofmobility management (MM) is extended to introduce another state the socalled the MM Offline state. The finite state machine with alltransitions is presented FIGS. 3a and 3b , which provide schematicdiagrams illustrating examples of state machines implementing theoffline state associated with embodiments of the present invention. Itwill be understood that the “attached” state collectively representseither the connected state or the idle state. FIG. 3a shows an exampleof a state machine operating at the network (i.e. the VMME and MME) foran individual communications terminal. FIG. 3b shows an example of astate machine operating at the communications terminal. As can be seenfrom FIGS. 8a and 8b , the states at both the communications terminaland the network transition from the detached state to the attached oroffline state when the communications terminal is powered on. Thereverse occurs when the communications terminal is powered off.Transitioning from the offline state to the attached state can betriggered by network notification, such as a paging message or by thecommunications terminal if there is any pending uplink data to be sent.

One should bear in mind that in the conventional system two instances ofthese state machines reside in the system i.e. at the communicationsterminal and in the MME/SGSN. In this invention there might be more thentwo instances of this state machine when the communications terminal isin the MM_Offline state i.e. at the communications terminal and, at allVMME associated with the PDN-GW(s) the communications terminal use(s)(in total 2+).

These MM states are characterised in the following way:

MM-Detached:

MM-detached: the communications terminal's location is not known and assuch the communications terminal cannot be contacted. It is understoodthat the communications terminal is not reachable.

MM-Attached:

MM-attached: the communications terminal is registered in the system andit is understood that the communications terminal is reachable. Legacymethods are used to track the communications terminal location in theIDLE mode (i.e. the tracking area update procedures in the LTE/EPCsystem) and in the connected mode (handover procedures)). The IP addressis allocated (or not if the UMTS/GPRS is used which required the PDPcontext to be established).

When the communications terminal is moved to the MM_Offline state, theMME used the GTP-C protocol to release the S5 bearer(s) towards thePDN-GW and push the MME context onto the VMME (or VMMEs). The NAS andS1AP/RRC signalling are used to inform the communications terminal tomove to the MM_Offline state (NAS signalling is also required since anew GUTI/GUTIs are allocated)MM-Offline:MM-offline: In this state the following applies:

-   -   The communications terminal has the IP address(s) allocated    -   The context at the MME has been invalidated at the time of        communications terminal's transition to the MM_offline state.        Then the MM context is pushed to the VMME(s).    -   Optionally the communications terminal may be configured also to        notify its presence on periodic basis. For this purpose the        modified tracking area update procedure may be used. If the        communications terminal fails to do so, the PLMN the        communications terminal is using is declared as unknown    -   No legacy tracking area update procedures are used when the        communications terminal moves between location areas (LAs)    -   The NAS signalling is used to move the communications terminal        to the MME_Offline state the paging or other notification        methods can be used to move the communications terminal out of        this state.    -   In this state the communications terminal is not allowed to        trigger any NAS ESM (EPS session management) procedures.    -   The communications terminal if authorised by the network may be        allowed to request to be moved to the attached state. This is        typically the case when the UE has some pending data to be sent.

The communications terminal must be in the MM_Attached state in order tobe able to move to the MM_Offline state. Once the communicationsterminal is in the MM_Offline state the only possible transition is tothe MM_Attached state.

In the MM_Offline state the communications terminal does not update thenetwork with its current location. However the communications terminalmay be able to listen to the broadcast channel or paging channels whichwould typically require a very long DRX cycle.

Terminal may not be required if configured to check its presence in thehome PLMN the frequency of which is defined by a timer value. In generalboth parameters (the PLMN check timer value and the DRX cycle) areconfigurable by the operator (per communications terminal or per system)and they depend on particular operator constraints and deployments orthe communication terminal's subscription information.

The communications terminal may be triggered by the network to move tothe MM_ATTACHED state by the notification procedure. The communicationsterminal may also autonomously decide to move to the MM_ATTACHED stateif some triggering conditions are met. However the terminal must seekthe consent of the network to do so. The communications terminal wouldtypically use the modified version of the NAS Service Request message.

In some cases the communications terminal may remember whether the powerwas switched off while the communications terminal was in the MM_Offlinestate or not. That will have impact on the procedures triggered when thepower is switched on. This feature may depend on the communicationsterminal category/capabilities or be based on the subscriptioninformation or system configuration. This can be communicated during theattach procedure. An advantage is therefore provided because acommunications terminal can avoid scenarios when frequent power on/offgenerates excessive signalling in the network.

Globally Unique Temporary Identifier

When a communications terminal first registers with the network (and istherefore either in the idle or connected state) an IP address is passedto the communications terminal 103 by the PDN-GW 105 (the IP address maybe allocated by the PDN-GW or the external network i.e. the ISP) and aGlobally Unique Temporary Identifier (GUTI) is allocated to thecommunications terminal 103 by the MME 106. The PDN-GW 105 stores the IPaddress and the MME 106 stores the GUTI. The composition of aconventional GUTI is shown in FIG. 4. As can be seen, the GUTI comprisesa first portion 201 that uniquely identifies the MME 106 and a secondportion 202 that uniquely identifies that communications terminal 103.The first portion includes a MME identifier 203.

A Globally Unique Temporary Identity (GUTI) is used to provide anunambiguous identification of a communications terminal that does notreveal a user's permanent identity in the Evolved Packet System (EPS).It is also used to identify the serving MME and network.

The GUTI is allocated when the communications terminal is being attachedto the system. It is proposed that the GUTI is also used for the purposeof the communications terminal identification during paging and for thepurpose of routing of the C-Plane signalling to the appropriate nodes inthe system when the terminal is in the offline state. This might requireupdating of the existing routing functions in the system e.g. at theeNB, MME, SGW. However as explained above, when the communicationsterminal moves to the MM_Offline state, a new GUTI is allocated by theVMME and is used in all signalling initiated by the communicationsterminal or the network e.g. location updating procedure and the paging.This location updating procedure has been overloaded from a functionalpoint of view as it does not indicate the communications terminalpresence in a particular location area (LA) but merely serves as theindication that the terminal still resides in the PLMN. This procedureis used if the communications terminal has been requested to indicateits presence in the PLMN periodically. The GUTI is included in theTracking area Update request message. A GUTI has good propertiesidentifying not only a communications terminal but network entities aswell as the country and the PLMN to which the communications terminalhas been attached. When the communications terminal triggers theLocation Update procedure, the U-plane bearers are not allocated (i.e.The Tracking Area Update Request message) in the MM_Offline state. Asexplained above, when the communications terminal enters the off-linestate the old GUTI is replaced by a new GUTI allocated by the VMME.

When a communications terminal moves to the MM_Offline state, the MMcontext is moved to other network entities. The old GUTI which isallocated by the MME for communications terminals in the MM_Attachedstate could potentially be allocated by any other MME to anothercommunications terminal. This re-allocation of the same GUTI could causeproblems when the communications terminal in the MM_Offline state ismoved back to the MM_Attached state in the area controlled by the sameMME. To resolve this problem embodiments of the present techniqueoperate as follows:

-   -   Once the communications terminal is moved to the MM_Offline        state the GUTI is modified    -   The MME Code is changed to indicate a virtual MME    -   The MME Group Id is modified to reflect a virtual MMEs group.    -   A new M-TMSI is allocated by the VMME.

The virtual MME Group/MME Ids shall not be used by real MMEs/MME groups.

A new GUTI is allocated by a new serving MME when the communicationsterminal is moved back to the MM_Attached state. When the MM context ismoved to the VMME (PDN-GW), the MME/MME group Ids in the GUTI areupdated and a new M-TMSI is allocated. These new GUTIs are communicatedto the communications terminal in the NAS messages. Allocatingidentities (i.e. MME/MME group Ids) to virtual components helps to routesignalling to these components.

Communications Terminal Operation

A Communications terminal may be arranged to enter the offline state dueto any appropriate circumstance. For example, if the communicationsterminal forms an MTC type device, it may be arranged to remain in theoffline state at all times unless it is sending or receiving data. Inother examples, communications terminals may be arranged to enter theoffline state when triggered by an event such as an amount of availableenergy within an internal power supply dropping below a threshold level.In other examples, the communications terminal may be arranged to enterthe offline state on receipt of a command from the network. In yetfurther examples, the communications terminal may be arranged to remainin the offline state unless it is sending or receiving data or adetermination is made either at the communications terminal or thenetwork that the communications terminal should enter the attached statein order that its location be tracked by the network so that it canreceive paging messages more quickly than it would do were it in theoffline state.

Typically when a communications terminal is in the offline state itwould not need to update the network with its current location. However,in some examples the communications terminal may optionally indicate itspresence in the network i.e. to indicate its presence in the PLMNperiodically in a similar manner to the legacy periodic trackingarea/location updating procedure. However, the communications terminalwould indicate its presence in the PLMN and optionally signal thecurrent local area/tracking area LA/TA. In some examples thecommunications terminal triggers this procedure when it crosses atracking area boundary of an outer boundary of a predetermined set oftracking areas. This is because a time interval between consecutiveupdates is much longer than for conventional communications terminalsperforming periodic tracking area/location updates. The interval betweentracking area/location area updates at which this happens can be aconfigurable parameter linked with the communications terminalsubscription.

In another example, when in the offline mode the communications terminalis arranged to detect when it leaves the network in order to trigger alocation update procedure to register in a new PLMN. However, due tolower probability of this event occurring, for example when an operatorhas coverage over a large geographical region, the communicationsterminal may not be required to check its presence in its home networkfrequently. The frequency with which the communications terminal checksits presence can be configurable by the network operator.

As explained above, the communications terminal can be triggered by apaging message to move to the attached state by the paging procedure.However, in some examples, the communications terminal may alsoautonomously decide to move to the attached state if various triggeringconditions are met such as pending transmission of uplink user data.However in the latter example the network must express its consent forthe terminal to do so.

In some examples the DRX (Discontinuous Reception) cycle used by thecommunications terminal (i.e. the periodicity with which the pagingchannel is monitored) is configurable. For example, to conserve power, arelatively long DRX cycle can be used. On the other hand, to check forpending downlink data more frequently a shortened DRX cycle can be used.Typically, longer DRX would be used for the communications terminals inthe offline state. This can be done by the HPLMN and typicallycommunicated to the communications terminal when it is commanded to moveto the offline state. The paging occasions the communications terminalneeds to monitor depend on its IMSI as well as the DRX parametersconfigured by the PLMN beforehand.

It also shall be noted that the communications terminal while in theMM_Offline state may listen to new channels to receive notifications forexample:

-   -   Special BCCH information e.g. new SIB with low periodicity    -   A new paging channel    -   An existing paging channel    -   The CBC (Cell Broadcast System)    -   The MBMS e.g. the MCCH or MTCH channel

The communications terminal may be able to search and discriminatewhether any of these means is available usually by listing to the BCCHinformation where the supported features are advertised/broadcasted.

When in the process of making transition to the MM_Attached andConnected states, the communications terminal receives the RRC requestto establish SRBs and data bearers as well the NAS message. A new GUTIis allocated via the NAS signalling exchange. The old GUTI is discarded.

The communications terminal may also be told during the NAS signallingexchange whether it shall move back autonomously to the MM_Offline ornot when the current data exchange has been completed.

In some examples the communications terminal may be configured toconfirm periodically the PLMN it is currently in. Typically on theexpiry of the timer the communications terminal is required to triggerthe modified tracking area update procedure (This feature is equivalentto periodic tracking area update but now the scope of this update is thePLMN and not the current Location area (LA)).

As explained above with reference to FIG. 2, notification can betriggered by the U-Plane data arrival 340 or by the C-plane signalling330 coming from the external entity. The former solution is desirable asthe application server does not need to have additional complexity tohandle and co-ordinate the paging/notification procedure.

Also the communications terminal in the Offline state still has the IPaddress allocated due to the introduction of the new MM-Offline state sothe PDN-GW seems to be a suitable entity to be the first point ofcontact for data arriving to the PLMN. One advantage is that thisarchitecture is linked with the subscription controlled by the PLMN.

The C-Plane approach requires the trigger to come from the externalentity residing for example an application server. This requires thatthe application server has can reach the communications terminal. Theformer (i.e. the U-Plane based triggers) approach conceals thisinformation from the application server as there is no need to discloseit to the application server because the PCE is managed by the HPLMN.

Network Operation

When the network pages the communications terminal in the MM_Offlinestate the following steps happens:

-   -   If the PLMN is known the VMME at the PDN-GW in the home PLMN        triggers paging in MME(s) in the HPLMN    -   The paging id used is S-TMSI if some MME codes are globally        reserved for Virtual MME or the paging id is extended to include        also the MMEGI    -   The MME(real) just forwards the paging message to eNBs.    -   The communications terminal searches for the S-TMSI or STMSI and        MMEGI depending on the operator's policy for the allocation of        internal system identifiers.    -   The MME is a stateless device and forwards/routes the        communications terminal's response to the VMME (the PDN-GW if it        is co-located) including its own address.    -   The VMME based on this address pushes the MM context onto this        real MME which selects the S-GW and triggers the process of the        s5 bearers establishment. Upon successful establishment of these        bearers the VMME(s) delete the MM Context(s). The real MME is        also establishing the S1 bearers and RRC connection (SRBs) which        triggers the communications terminal to move to the        MM_Registered and ECM-Connected states.    -   The MME allocated a new GUTI, the old one is deleted    -   The communications terminal discards the old GUTI(s) when a new        one has been allocated.    -   Finally the Data Radio Bearers are established if the network        deems it necessary.

If the communications terminal has been configured to provide a periodicPLMN update, the network assumes that the communications terminal's PLMNis unknown if no update has been sent be the communications terminal.When the communications terminal provides the PLMN update, only thefirst VMME at the PDN-GW is contacted. Alternatively all the VMME(s) arecontacted. If the former option is used and there are multiple PDN-GWsused, the contacted VMME and its PDN-GW informs other VMME(s) that theupdate has been received.

The description provided so far has dealt with the scenario when thepaging is triggered by the U-Plane data arriving to the anchor pointi.e. the home PDN-GW(s). However the application server might alsotrigger the paging. In this scenario the server might be managed by thethird parties. The PLMN-GW is used to trigger the paging. The PLMN-GWrequests the VMME(s) to coordinate the paging in a similar way as in thescenario described above. The applications will not typically use theIMSI but another communications terminal identity which the PLMN can maponto communications terminal's IMSI. The amount of information which isavailable to the application may be restricted unless the operator willdisclose it to the third parties. When the notification procedure e.g.the paging was successful the PLMN-GW informs the application serverabout it and may also send some auxiliary information.

The PLMN-GW needs to obtain information from the HSS about the mappingbetween the id and the IMSI and the address of the VMME associated withthe first PDN connection which has been established at the attach time.This VMME will be used to co-ordinate the paging

Alternative Implementation

It is also possible to arrange the system to have just one VMME alwaysassociated with the first PDN connection and PDN-GW. Other PDN-GW(s) ifused, for example several PDN connections and IP addresses could betriggered by the U-Plane data. In this case the PDN-GW needs to findrouting information, generate and forward the C-Plane trigger to theVMME. This is possible as all PDN-GW could store the information aboutthe address of the VMME associated with the first PDN connection inorder to be able to locate the VMME. An advantage is that just one GUTIis allocated also in the scenario when several PDN-GWs are used and thecommunications terminal needs to monitor just one paging identity whenin the MM_Offline state.

When the MME moves the communications terminal to MM_Offline state, itneeds to release the S5 bearers to the PDN-GW(s) and this signalling(the GTPC signalling) can be used to update this piece of information inall involved PDN-GWs.

As for the network operation mentioned above paging can be triggered bythe U-Plane data arriving to the anchor point i.e. the Home PDN-GW.Alternatively the application server using the C-Plane can also triggerthe paging via the intermediary entity called the PLMN-GW. Theapplication server is typically managed by the third parties. ThePLMN-GW requests the VMME to initiate and coordinate the paging in asimilar way as in the scenario described above. The only difference isthe application server may not use the IMSI but another communicationsterminal identity which the PLMN can translate to communicationsterminal's IMSI. Also the amount of information which is available atthe application server may be restricted unless the operator willdisclose it to some third parties. When the paging was successful thePLMN-GW informs the application server about it and sends someinformation (e.g. the IP address) allowing the server to send data tothe communications terminal via the PDN-GW. Alternatively small amountof data may be delivered together with the trigger indication.

Summary of Operation

According to example embodiments of the present technique, the operationof the network and the communications terminals in accordance with theprocedures described above, which form example embodiments aresummarised by the call flow diagrams provided in FIGS. 5a, 5b, 6a, 6b,7a and 7b . Furthermore diagrams illustrating the active and passivestate of some of the core network entities of FIG. 2 when acommunications terminal is in the off-line state and the attached stateare provided respectively in FIGS. 8 and 9.

FIGS. 5a and 5b form together a flow diagram illustrating the operationof the various elements of the mobile communications system as thecommunications terminal 103 moves from an attached state to an offlinestate. The mobile communications terminal 103 could be in either anattached state, an idle state or a connected state, but for any of thesestates actions which need to be performed by the network elements tomove the communications terminal to the off-line state a as explainedabove are summarised by FIG. 5.

As shown in FIG. 5a , at step 1 the network makes a decision to move thecommunications terminal 103 to the offline state. This can be based on auser's inactivity period, subscription information or a function ofsystem load or a combination of the user inactivity and/or subscriptioninformation. The entity which makes the decision could be the following:

-   -   The MME 106;    -   The PDN-GW 302 with support of the PCC system, then the PDN-GW        302 requests from the MME 106 via the S-GW 104 to move the        communications terminal to the offline state; or    -   A combination of the MME 106 and the PDN-GW 320, which may        negotiate, for example, in the roaming architecture the MME may        not be capable of this functionality or VMME may have some local        policies and the Home PDN-GW 302 may support this functionality        or have another set of rules imposed by the home operator so        some form of negotiation is required.

Supposing that the network has made the decision to move thecommunications terminal to the offline state. The serving MME 106 isresponsible to coordinate the communications terminal's MM contexttransfer to the Virtual MME (s) 301. There are two variants of thesolution, which are presented in the flow diagram, which are:

-   -   Variant 1: For each PDN-GW 302 used by the communications        terminal there is one VMME 301. In that case the MME 106        requests the PDN-GW 302 via the S-GW 104 to request from its        associated VMME 310 to establish the communications terminal's        MM context based on the context information provided by the        serving MME 105. This leads to the establishment by the PDN-GW        302 of the communications terminal's 103 dedicated signalling on        the Sx′ interface with its VMME 301. The PDN-GWs 302 also marks        the communications terminal's 103 as in the offline state. The        VMME(s) 301 confirm to the serving MME 106 that the context has        been established including the GUTI (s) allocated for the        communications terminal 103.    -   Variant 2: If there is just one VMME 301 by agreement it is        assumed that it is associated with the PDN-GW 302 which is used        for the first PDN connection established by the communications        terminal 103. In this case the initial signalling is the same as        in variant 1 but the VMME 301, based on the communications        terminal's MM context information, requests from other PDN-GWs        302 to mark the communications terminal 103 as offline and        establish the communications terminal's 103 dedicated signalling        over the Sx′ interface. Each PDN-GW 302 used by the        communications terminal will have means to contact the VMME 301        (one for the communications terminal). The VMME 301 confirms to        the serving MME 106 that the context has been established        including a new GUTI allocated for the communications terminal.

Thus referring back to FIG. 5a , at step S2 the communications terminal103 is in the attached and connected state. At step S2 the MME istriggered from the PDN-GW or the MME makes an internal decision to movethe communications terminal to the offline state. The MME may decide tomove the Communication terminal 103 to the offline state based on therequest sent by the communication terminal 103 in a NAS message or otherinternal factors such as communication terminal inactivity time,operator's policies and user subscription information. Step S2 includestwo possibilities for triggering the move to the offline state. In stepS2.1 the decision is made by the MME 106 whereas in step S2.2 thedecision is made by the PDN-GW either on its own or based on a triggerfrom the PCC. If the decision is made in the PDN-GW 302 then messagesexchanges M1 and M2 follow in order to communicate to the MME 106 thatthe communications terminal 103 should move to the offline state.

In step S3 (variant 1) the UE's Context information including PDNconnection information for the communications terminal is moved to theVMME 301. However, as explained above, the communications terminal 103could have one or a plurality of PDN connections and moreover maybeserved by different VMMEs. As such for each PDN connection a differentPDN-GW and its associated VMME may be used, Another alternative (variant2) is that one VMME 301 is used in the system regardless of the numberof PDN-GWs then all of the PDN-GWs which have established connections tothe communications terminal are updated with the information that thecommunications terminal 103 is offline and the address of the VMME isprovided to the PDN-GWs by the MME 106. If there is more than onegateway then the VMME 301 associated with the PDN-GW for the first PDNconnection is used and the context information in other PDN-GWs areupdated as explained above. To this end, a message exchange followswhich includes M3, M4 and M5 to establish a UE's context in the VMME 301via the PDN-GW. At this point in step S3.1 the Sx′ interface is createdand a communications terminals context is communicated to the VMME 301from the MME 106.

In message M6 the VMME 301 confirms that the context information hasbeen established and then proceeds to issue a new GUTI. In step S3.2 theinterface Sx′ is established and the context information is updated atthe PDN-GW with an indication that the communications terminal isoffline. The PDN-GW 302 then confirms to the MME 106 via messages M7, M8that the context has been established within the VMME 301 and passes thenew GUTI of the communications terminal 103 which has been issued andagainst which context information for the communications terminal 103 isstored.

If the communications terminal 103 is in the idle state then it needs tobe moved to the connected state (at S5) and this is performed in stepS4. This is realised in step S4.2 where the communications terminal 103is paged to move the communications terminal to the connected state (inLTE this is the ECM_Connected state) and establish NAS connectivity atS5. This is required in order to enable the serving MME 106 to send theNAS command to move the communications terminal to the offline state.The NAS command will also include the GUTI allocated by the VMME(variant 2) or GUTI(s) allocated by the VMME(s) in variant 1. The NASmessage may also be used to communicate other parameters to be used bythe communications terminal such as e.g. very long DRX values applicableto the offline state.

As explained above, the MME 106 issues a NAS command to thecommunications terminal 103 to move to the offline state. This iseffective with a message M9 which includes the GUTI of thecommunications terminal 103. Using a message M10 the NAS command isconfirmed by the communications terminal 103 to the MME 106.

As for the step S3 in step S6 (variant 2) for each PDN connection ifdifferent PDN-GWs are used steps are performed in order to move thecommunication terminal's context to the VMME 301. Thus, in step S6.1 thecommunications terminal's 103 context is deleted from the MME 106 and aGTP-C message M11 is communicated to the serving gateway 104 which alsodeletes the communications terminal's context in step S6.2 whichincludes the s11 and s5 bearers. A message M12 is then sent to thePDN-GW 302 to confirm that the communications terminal 103 has moved toan offline state and in steps S6.3 and S6.4 the PDN-GW deletes the s5bearer and confirms that the communications terminal has moved to theoffline state to the VMME 301 via message M13 and the VMME 301 in stepS6.4 completes the establishment of the Sx′ interface.

In step S6, upon the receipt of the confirmation from the communicationsterminal 103, the serving MME 106 is responsible for confirming to thenetwork entities that the communications terminal 103 has been moved tothe offline state. That leads to the removal of the communicationsterminal's context information from the SGW 104, deletion of the s5bearers established for the communications terminal, deletion of anycommunications terminal's identities allocated for the s11 interface.Finally the serving MME deletes the communications terminal's contextinformation, and the communications terminal is considered by thenetwork to be in the MM off-line state in step S7.

It should be noted that there are slight differences for variant 1 andvariant 2 solutions, which are:

-   -   Variant 1: The MME notifies all PDN-GW(s) which notify its        associated VMME(s).    -   Variant 2: The MME notifies all PDN-GW(s). The PDN-GW(s) will        notify the VMME in the system (the same node notified by 1 to        many PDN-GW(s))

Thus at the end of the flow diagram shown in FIGS. 5a and 5b at step S7the communications terminal is in the offline state.

FIGS. 6a and 6b provide a flow diagram which together illustrate theprocess in which the communications terminal moves from an offline stateto an attached state. Thus as shown in FIG. 6a the flow diagram startswith the communications terminal 103 in the offline state at state S10.When the communications terminal is offline the trigger to move theattached state may come from the network or the communications terminal103 itself. The latter may be subject to the operator's authorisationand policies. The network initiated trigger may come as the C-Planetrigger or U-Plane (any data arriving at the PDN-GW). In the latter casethe PDN-GW checks whether the communications terminal is offline. Thisis realised by checking whether the match has been found in the TFTfilters established for the communications terminal 103 which has beenmarked as being in the offline state. Then the PDN-GW requests the VMME301 providing its address (in variant 1 it is the VMME associated withthe PDN-GW, in variant 2 it is the VMME associated by convention withthe first PDN connection and its PDN-GW) to initiate and supervise thepaging procedure (S13.1 and M25). If the C-Plane trigger is received,the PLMN-GW is used to convey the trigger to the VMME 301 (via thePDN-GW 302 or directly) which initiates the paging procedure asexplained above. Note that the VMME used for the first PDN connection isalways used in variant 1 and 2. The PLMN-GW obtains information aboutthe address of the PDN-GW (or alternatively the VMME) from the HSS.Alternatively the VMME may update the PLMN-GW with this information whenthe communication terminal 103 is moved to the offline state. The VMMEinitiates and supervises the paging procedure (note that pagingstrategies may be applied to minimise paging load in the system). TheVMME includes the PDN-GW address and the GUTI in the paging request sentto the MME(s). Therefore as shown in FIG. 6a , process steps S11 and S12illustrate these two arrangements via which the communications terminalmay be required to move to the attached state which are respectively viaa U-plane trigger or a C-plane trigger. In the U-plane trigger U-planedata is received via message M20 which is communicated to the VMME 301via an internal C-plane trigger using an address obtained from thePDN-GW 302 in message M21. For the C-plane example a C-plane trigger isreceived by a PLMN gateway 400 from an external network 401 which ismessage M22 and via messages M23, M24 an internal C-plane trigger iscommunicated from the PLMN-GW to the PDN-GW 302 and from the PDN-GW 302to the VMME 301.

In step S13 the communications network pages the communications terminalwhich is in the offline state so that it can be moved to the attachedstate. Various paging strategies maybe used. In one example, the MME(s)requests from the eNode B(s) 102 to page the communications terminal103.

In the example illustrated in FIG. 6a paging for only one MME ispresented. Thus, in step S13.1 the VMME 301 having received the triggerstarts the paging supervision process in step S13.1. The paging istriggered via messages M25 by the VMME 301 contacting each of theavailable MMEs 106 within the network to trigger paging using the GUTIprovided by the VMME and the PDN-GW address. The MME(s) 106 send apaging message M26 to the eNodeBs 102 which trigger a paging of thecommunications terminal 103 via messages M27 to the communicationsterminal 103. The communication terminal 103 after detecting that it isbeing paged (detecting its S-TMSI and optionally MMEGI) respondsrequesting the establishment of the RRC connection and sending the NASservice request message in the RRC connection setup complete messageM28. At step S13.2 the eNode B 102 routes a request to the MME whichsent the paging request. The eNode B 102 then sends a message M29 to theMME 106 which sent the paging message to communicate the content of theNAS service request message M28 to the MME containing the S-TMSI and theMMEGI supplied by the communications terminal 301 and in response theMME 106 creates an initial context for the communications terminal isstep S13.3. The NAS service request message includes the S-TMSI andMMEGI (the MMEGI is optional in some deployments if just one VMME isused). The MMEGI and S-TMSI are used by the MME 106 to route theresponse of the communications terminal to the VMME. In the deploymentscenario when just one VMME is used the MMEGI is not required.Alternatively the PDN-GW address can be used to route the response tothe PDN-GW which can forward the response to the VMME.

In step S13.4 the MME 106 arranges for the SGW 104 to allocate a bearerfor communicating to the communications terminal 103 via messageexchanges M30 and M31 the communications terminal's S11 interfaceidentities and communications bearer s5 are established and at stepS13.5 the serving gateway performs the process of establishing the s11and s5 interfaces. In step S13.6 the PDN-GW allocates further componentsfor the U-Plane path (e.g. the GTP-U TEID) and routes (based on theS-TMSI and MMEGI) the message M32 to the VMME 301. Accordingly, at stepS13.7 the VMME stops the supervision of the paging of the communicationsterminal and retrieves the context based on the S-TMSI which it hasreceived from the PDN-GW 302 and using a message M33 the VMME 301communicates the context of the communications terminal to the PDN-GW301.

Once the communications terminal 103 responds to the paging procedure,the eNode B 102 routes the response to the default MME (this is the MMEwhich has initially sent the paging request to the eNode B). The MMEcreates the initial context, selects the S-GW and establishes the s11interface for the communications terminal 103 (allocates TEIDs to beused by the communications terminal). The MME 106 sends to the SGW 104the request for the old communications terminal's context informationincluding the PDN-GW address. The SGW forwards the request to the PDN-GW(based on the PDN-GW address or the MMEGI+S-TMSI) establishing partiallythe s5 bearers for the communications terminal. The PDN-GW forwards therequest to the VMME which stops paging supervision and the VMMEretrieves the communications terminal's old context based on the S-TMSI.The VMME responds to the request and sends the old communicationsterminal's context to the MME via the PDN-GW and the SGW. This allowsthe s5 bearers and the s11 interface to be fully established for thecommunications terminal. The VMME deletes old communications terminal'scontext information as well as the communications terminal's identitiesallocated for the Sx′ interface.

The re-establishment of other remaining s5 bearers for other PDN-GW maybe done in two ways:

-   -   Variant 1:        -   The VMME contacts other VMME if they exist. The other VMME            will trigger the associated PGW to re-establish S5. The S-GW            address is provided.        -   If there is just one VMME and several PGW the VMME triggers            other PDN-GW to establish the S5 with the S-GW    -   Variant 2:        -   The MME is responsible for the re-establishment of all other            S5 bearers with other PDN-GW based on the communications            terminal's context data received from the VMME(s).

Therefore as shown in FIGS. 6a and 6b , in step S14 the VMME deletes theSx interface and the communications terminal's context information whichit has stored and depending on the number of PDN connections which areavailable to the communications terminal the VMME 301 arranges foreither all of the PDN connections to be re-established and then deletestheir context or just PDN connection which is required and maintains thecontext for the other PDN connections.

In step S15 the Sx interface is deleted at the PDN-GW 302 and thecommunications terminal's context information is updated correspondinglyat the MME 106 which is serving communications terminal at step S16using messages M34, M35 from the PDN-GW 302 to the MME 106. Assumingthat the network has not reported any errors the MME 106 via messagesM36, M37 commands the communications terminal 101 to move to theMM_Attached and connected states. The old GUTI is not valid anymore andthe new GUTI which was allocated by the MME is provided to thecommunications terminal 103 in messages M36 and M37. Messages M36 andM37 also initiate the radio and S1 bearers establishment which uponsuccessful completion is confirmed and communicated to the MME 106 inmassages M38, M39. The messages M38 and M39 are also used to send a NASmessage confirming that the communication terminal 103 has beensuccessfully moved to the MM_Attached state.

It should be noted that the SOW 104 may pass its address in the messageto the VMME, if this VMME contacts other VMME(s) to re-establish the s5bearers (variant 1). The new serving MME establishes the fullcommunications terminal's context based on additional informationreceived from the VMME and allocates a new GUTI which is communicated tothe communications terminal in the NAS Command “Change state” messageover the S1AP Initial Context Request message and RRC reconfigurationmessage. The NAS command is confirmed by the communications terminal inthe NAS change state complete message which is carried in the RRCReconfiguration Complete and the S1AP Initial Context Setup Completemessage. The MME may also send a standalone NAS Command Change Statemessage to the communications terminal encapsulated in the S1AP DL NAStransport message. The communications terminal responds with thestandalone message as well. This is to enable the MME to triggersecurity procedures (the Authentication and security mode controlprocedures) and then the S1AP initial Context Setup procedure is used tore-establish all data radio bearers and the S1-U bearers for thecommunications terminal. From that moment the communications terminalcan be considered as in the attached and connected states (in LTE it isthe EMM_REGISTERED and ECM_CONNECTED states) at step S17.

FIGS. 7a and 7b provides a call flow diagram illustrating an exampleembodiment of the present technique in which the communications terminalprovides the communications network with an update of its presence andlocation when in an off-line state.

Starting at step S18 with the communications terminal in the offlinestate, at step S19 the communications terminal 103 is arranged toperiodically notify the mobile communications network of its presenceafter an update timer expires. Accordingly, the communications terminaltriggers the presence update procedure which by implementation uses thetracking area update procedure which has been modified to indicate acommunications terminals presence to the network which needs to benotified periodically. The communications terminal includes theS-TMSI(s) in an update message and MMEGI(s) if available. In additionthe communications terminal 103 also provides its current location i.e.the tracking area. An eNode B receiving the message routes the messageto the default MME 106. The default MME 106 based on the S-TMSI(s) andMMEGI(s) if available routes the request to the VMME(s) 301 whichupdate(s) its PLMN periodic timer. The VMME 301 acknowledges the requestto the communications terminal 103 in the tracking area accept message.The VMME(s) 301 may re-allocate GUTI(s) and pass them/it in thismessage. The communications terminal is required to acknowledge thereceipt of the message only if a new GUTI/GUTIs has/have been allocated.This is realised in the tracking area update complete message.

Accordingly, as shown in FIG. 7a , a message M40 is sent from thecommunications terminal 103 to the eNode B 102 providing an NAS messagewhich includes a tracking area update. The eNode B 102 uses a defaultrouting of the NAS message M40 to the MME in step S20 to route a messageM41 providing the tracking area update as a NAS message to the MME 106.In step S21 the MME routes to the VMME 301, based on the S-TMSI andMMEGI, if present the tracking area update message which is communicatedto the VMME 301 via a message M42.

In step S22 the VMME 301 restarts a periodic communications networkupdate timer. If this timer expires the communications terminal isimplicitly detached after some grace period and moved to a de-registeredstate.

Optionally In step S23 further updates of the communication terminal'slocation is provided to the other VMMEs 301 as identified by S-TMSIs andMMEGIs which have been provided by the communication terminal 103 to theMME 106 in messages M40 and M41. The VMME 301 in each case provides aNAS message providing a tracking area accept message M43 to the MME 106.Alternatively the tracking update message is sent only to the VMMEassociated with the first PDN connection and PDN-GW and the VMME isrequired to update other VMME(s) if they exist.

Depending on arrangements in step 23 as shown in step S24 the VMME(s)may communicate the NAS tracking area accept message(s) to MME but thismaybe

-   -   just from one VMME 301 associated with the first PDN connection        and PDN-GW established by the communication terminal 103 at the        attached time which is used to provide the NAS tracking        acceptance and the VMME correspondingly notifies all other        parties. Using messages M44, M45, M46 and M47 the NAS tracking        area accept message is transported in the S1AP Downlink        transport and RRC message via the eNode B 102 to the        communications terminal 103.    -   From all VMME(s) associated with PDN connections and PDN-GW(s).        In this case the MME 106 waits for all responses in order to be        able to transmit new GUTI(s) to the communication terminal 103        if allocated in the NAS tracking area accept messages M44 and        M45.        If new GUTI(s) has/have been allocated the NAS Tracking Area        Complete message is transmitted by the communications terminal        103 in messages M46, M47 to the MME 106. Correspondingly (a) NAS        tracking area update complete message(s) M48 is/are communicated        to the VMME or VMMEs depending on the option employed in step 23        and in step 24. The communication terminal 103 and the network        (the MME 106) shall be considered to be in the MM_Offline and        connected state (S25)

In step S26 there is optionally the step of subsequent forwarding of thecompletion of the NAS tracking area updates to the VMME(s). At the endof the flow diagram step S27 indicates that the communications terminalis still in the offline state even though its presence and location hasbeen updated to the mobile communications network.

It should be noted that the communications terminal 103 needs to includeS-TMSI(s) and MMEGI(s) if available in order to allow the MME 106 toroute the response to the VMME(s). These identities are sent in the RRCmessage and S1-AP message because the NAS is encrypted and the MME assuch cannot access ut/them and other IEs contained in the NAS message.

FIG. 8 provides a schematic illustration of mappings of core networkentities of a communications network corresponding to the example shownin FIG. 2, for an example in which the communications terminal entersthe off-line state. As shown in FIG. 8, there are three variants A, B1and B2 which represent three possible architectures of the core networkpart of the mobile communications network of example entities which areserving the mobile communications terminal which has entered theoff-line state. In the variant A, the mobile communications terminalwhich has entered the off-line state has, when in the attached state,available to it three PDN connections via three different PDN-GWs, whichare identified as PGW1 302.1, PGW2 302.2 and PGW3 302.3. As explainedabove, when the mobile communications terminal enters the off-line statepart of the context information which is required to re-active thecommunications bearers, which have been used by the communicationsterminal are communicated from the MME 106 to the VMME 301. The contextinformation stored may not correspond to the complete contextinformation which was held at the MME 106 but a sub-set of thisinformation. Furthermore the context information communicated to theVMME for storing in association with an identifier of the mobilecommunications terminal is sufficient to restore one or all of thecommunications bearers to any of the PDN connections PGW1 302.1, PGW2302.2 and PGW3 302.3, when the mobile communications terminal moves fromthe off-line state to the attached state. As such, if any of the PDN-GWsPGW1 302.1, PGW2 302.2 and PGW3 302.3 receives for example, U-plane datafor communication to the mobile communications terminal in the off-linestate, then the PDN-GW PGW1 302.1, PGW2 302.2 and PGW3 302.3 whichreceives the U-plane data contacts the VMME 301 in order that the VMMEcan instigate communication with the mobile communications terminal tomove the terminal to the attached state. Thus the first of the PDN-GWsto receive U-plane data for the communication terminal instigatescontact with the VMME 301 in order to trigger the process of paging themobile communications terminal in order to cause the mobilecommunications terminal to change from the off-line state to theattached state.

The variants B1 and B2 also shown in FIG. 8 provide alternativeexamples. In variant B1, a VMME 301.1, 301.2, 301.3 is provided for eachPDN-GW PGW1 302.1, PGW2 302.2, PGW3 302.3, so that in this example thePDN-GW which receives U-plane data for communicating to the mobilecommunications terminal via a PDN connection provided through the PDN-GWPGW1 302.1, PGW2 302.2, PGW3 302.3 will instigate communication with themobile communications terminal by contacting its own VMME 301.1, 301.2,301.3. Variant B2 presents a similar example, but does not provide a oneto one correspondence between PDN connections and PDN-GWs PGW1 302.1,PGW2 302.2 and PGW3 302.3, because PDN-GW 302.1 serves two PDNconnections 1 and 2, whereas the PDN-GW2 serves the PDN connection 3.However each of the two PDN-GWs PGW1 302.1, PGW2 302.2 has connected toit a VMME 301.1, 301.2 which is arranged to store the contextinformation for the PDN connections of the mobile communicationsterminals. Thus if U-plane data is received for communication to themobile communications terminal via either of the PDN connections 1 and2, then the first PDN-GW contacts the first VMME 301.1, whereas if datais received via the PDN connection 3 at the second PDN-GW3, then thePDN-GW3 contacts the second VMME2 301.2.

FIG. 9 provides an illustration of the three example variants A, B1, B2shown in FIG. 8, but showing the status of the entities when the mobilecommunications terminal has moved to the attached state. Thus as shownin FIG. 9, for each of the PDN connections 1, 2 and 3, whether providedby any of the three PDN-GW 302.1, 302.2, 302.3 and re-established by anyof the VMMEs 301.1, 301.2, 301.3, there is only one MME 106 and oneserving gateway S-GW 104, which is providing the PDN connections whenthe mobile communications terminal is in the attached state.

OTHER EXAMPLES

In accordance with the embodiments of the invention set out above,embodiments of the present invention can provide:

-   -   The mobility management (MM) in the 2G/3G or the EPS MM in the        LTE/EPS has been extended and a new state has been introduced,        which is the so called MM_Offline state.    -   The network has been arranged to restore the S5 interface (In        2/3G it is the Gn interface) without any further assistance or        at least reduced assistance from the communications terminal. In        normal circumstances the communications terminal needs to send        the PDN connection request (in LTE) or the PDP context        activation request in 2G/3G (also the network in 2G/3G may        request the MS/communications terminal to activate the context        by sending Request PDP context activation message)°    -   The NAS context does not need to be manipulated at the        communications terminal in order to establish (activate) bearers        and come out from the “offline” state i.e. no session management        procedures are required as it would have been if the        communications terminal had been moved to the de-registered        state.        The MM (or the EMM) communications terminal's context is pushed        onto the VMME upon transition to the “offline” state    -   Embodiments of the present technique find applications with        mobile communications networks which communicate data using the        UMTS/GSM standards. Furthermore embodiments also find        application to the MSC for the circuit switched services i.e.        calls with some adaptation on the GMSC instead of the PDN-GW and        VMME.    -   Note that in the detached state the PDN connection does not        exist at the PDN-GWN nor does at the GGSN. That means that there        is no communications terminal's context at the PDN-GW nor at the        GGSN. Due to the fact that there is no communications terminal's        context at the PDN-GW/GGSN, these nodes cannot map the ingress        IP flow onto the communications terminal (no TFT (traffic flow        template) filters are configured). Also note that the PDN-GW may        be used for the 2/3G system i.e. when the SGSNs are used which        can handle the S4 interface.    -   Some example EMM context data which are stored at the MME is        presented in the Appendix below. Only the subset of it would be        stored at the Virtual MME.

Various modifications may be made to the embodiments herein beforedescribed. For example embodiments of the present invention have beendescribed with reference to an implementation which uses a mobile radionetwork operating in accordance with the 3GPP Long Term Evolution (LTE)standard. However it will be understood that the principles of thepresent invention can be implemented using any suitable radiotelecommunications technology and using any suitable networkarchitecture in which shared communication bearers could beadvantageously employed for example GSM, GPRS, W-CDMA (UMTS), CDMA2000,and other mobile communication standards.

The invention claimed is:
 1. A communications terminal for transmittingdata to and receiving data from a mobile communications network, themobile communications network including a radio network part, a corenetwork part and a virtual mobility manager, the radio network parthaving a plurality of base stations arranged to transmit data to andreceive data from the communications terminal via a radio accessinterface, and the core network part including at least one packet datanetwork gateway arranged to route data to and receive data from the basestations of the radio network part via the core network and a mobilitymanager arranged to track a location of the communications terminalwithin the mobile communications network for routing the data to andreceiving the data from the communications terminal via the radionetwork part in accordance with context information of thecommunications terminal, the communications terminal comprising:circuitry configured to: transmit, via at least one of the base stationsto the virtual mobility manager, an indication that the communicationsterminal is entering an off-line state, the virtual mobility managerstoring at least part of the context information of the communicationsterminal in response to the indication; receive a paging message fromthe virtual mobility manager when the communications terminal is in theoff-line state and after occurrence of a triggering event, the pagingmessage indicating that the communications terminal should move to anattached state; and establish a communications bearer, with the mobilecommunications network after the communications terminal has moved tothe attached state, the communications bearer for communicating datawith the mobile communications network.
 2. The communications terminalas claimed in claim 1, wherein when the communications terminal is inthe off-line state, the communications terminal reduces an amount ofdata communicated to or received from the mobile communications network.3. The communications terminal as claimed in claim 1, wherein after thecommunications terminal enters the off-line state, the mobility manageris configured to detect that the communications terminal has entered theoff-line state, and to transmit the at least part of the contextinformation of the communications terminal with a first uniqueidentifier associated with the communication terminal to the virtualmobility manager, and the virtual mobility manager is configured to,after receiving the at least part of the context information from themobility manager, generate a second unique identifier, and thecommunications terminal is configured to receive the second uniqueidentifier.
 4. The communications terminal as claimed in claim 3,wherein the first unique identifier and the second unique identifier areglobal unique identifiers (GUTI).
 5. The communications terminal asclaimed in claim 1, wherein following the triggering event, thecircuitry is configured to receive the paging message, the pagingmessage including the identity of the communications terminal.
 6. Thecommunications terminal as claimed in claim 5, wherein the triggeringevent includes the packet data network gateway receiving data forcommunicating to the communications terminal.
 7. The communicationsterminal as claimed in claim 5, wherein the triggering event includesthe mobile communications network receiving control plane data forcommunicating to the communications terminal.
 8. The communicationsterminal as claimed in claim 5, wherein the circuitry is configured tomove from the off-line state to the attached state in response to a usercommand, and the triggering event includes the communications terminalmoving from the off-line state to the attached state.
 9. Thecommunications terminal as claimed in claim 8, wherein the triggeringevent includes the communications terminal moving from the off-linestate to the attached state in order to communicate data to the mobilecommunications network.
 10. The communication terminal according toclaim 1, wherein the circuitry is further configured to enter a detachedstate separate from the attached state and the off-line state.
 11. Amethod of communicating using a communications terminal via a mobilecommunications network, the mobile communications network comprising aradio network part, a core network part and a virtual mobility manager,the radio network part including a plurality of base stations arrangedto transmit data to and receive data from the communications terminalvia a radio access interface, and the core network part including atleast one packet data network gateway arranged to route data to andreceive data from the base stations of the radio network part via thecore network and a mobility manager arranged to track a location of thecommunications terminal within the mobile communications network forrouting the data to and receiving the data from the communicationsterminal via the radio network part in accordance with contextinformation of the communications terminal, the method comprising:transmitting, by the communications terminal via at least one of thebase stations to the virtual mobility manager, an indication that thecommunications terminal is entering an off-line state, the virtualmobility manager state storing at least part of the context informationof the communications terminal in response to the indication; receiving,by the communications terminal when the communications terminal in theoff-line state and after occurrence of a triggering event, a pagingmessage from the virtual mobility manager, the paging message indicatingthat the communications terminal should move to an attached state; andestablishing, by the communications terminal, a communications bearerwith the mobile communications network after the communications terminalhas moved to the attached state, the communications bearer forcommunicating data with the mobile communications network.
 12. Themethod of communicating as claimed in claim 11, further comprising:detecting, by the communications terminal, whether an amount of datacommunicated to or received from the mobile communications terminal hasreduced; and determining, by the communications terminal, whether thecommunications terminal should enter the off-line state according towhether the communications terminal has reduced the amount of datacommunicated to or received from the mobile communications network. 13.The method of communicating as claimed in claim 11, wherein after thecommunications terminal enters the off-line state, the mobility manageris configured to detect that the communications terminal has entered theoff-line state, and to transmit the at least part of the contextinformation of the communications terminal with a first unique identityassociated with the communication terminal to the virtual mobilitymanager, and the virtual mobility manager is configured to, afterreceiving the at least part of the context information from the mobilitymanager, generate a second unique identifier, and the method furthercomprising receiving, by the communications terminal, the second uniqueidentifier.
 14. The method as claimed in claim 13, wherein the firstunique identifier and the second unique identifier are global uniqueidentifiers (GUTI).
 15. The method as claimed in claim 11, furthercomprising after the triggering event, receiving the paging message bythe communications terminal, the paging message including the identityof the communications terminal.
 16. The method as claimed in claim 15,wherein the triggering event includes the packet data network gatewayreceiving data for communicating to the communications terminal.
 17. Themethod as claimed in claim 15, wherein the triggering event includes themobile communications network receiving control plane data forcommunicating to the communications terminal.
 18. The method as claimedin claim 15, wherein the method further comprises the communicationsterminal moving from the off-line state to the attached state inresponse to a user command, and the triggering event includes thecommunications terminal moving from the off-line state to the attachedstate.
 19. The method as claimed in claim 18, wherein when in theattached state, the communications terminal communicates data to themobile communications network, and the triggering event includes thecommunicating the data to the mobile communications network.
 20. Anon-transitory computer readable medium storing computer executableinstructions that, when executed by a communications terminal, causescommunications terminal to perform a method of communicating via amobile communications network, the mobile communications networkcomprising a radio network part, a core network part and a virtualmobility manager, the radio network part including a plurality of basestations arranged to transmit data to and receive data from thecommunications terminal via a radio access interface, and the corenetwork part including at least one packet data network gateway arrangedto route data to and receive data from the base stations of the radionetwork part via the core network and a mobility manager arranged totrack a location of the communications terminal within the mobilecommunications network for routing the data to and receiving the datafrom the communications terminal via the radio network part inaccordance with context information of the communications terminal, themethod comprising: transmitting, via at least one of the base stationsto the virtual mobility manager, an indication that the communicationsterminal is entering an off-line state, the virtual mobility managerstate storing at least part of the context information of thecommunications terminal in response to the indication; receiving, whenthe communications terminal in the off-line state and after occurrenceof a triggering event, a paging message from the virtual mobilitymanager, the paging message indicating that the communications terminalshould move to an attached state; and establishing a communicationsbearer with the mobile communications network after the communicationsterminal has moved to the attached state, the communications bearer forcommunicating data with the mobile communications network.